A DEVICE FOR DETECTING THE FOCUSED STATE OF AN OPTICAL SYSTEM

摘要

A device for detecting the focussed state of an optical system to determine whether the optical image of an object (25) to be photographed is in a correct focusing state to provide an image clearly formed on a predetermined image forming surface (22) through a photographic or image-forming optical system, using a single optical axis (7) to project light to the object and return reflected light to form an image, using a light projecting means and light receiving means (11, 12) in which apertures (15) small in diameter or width so formed and used that the structure is simple and compact.